1. Field of the Invention
The invention relates to an infrared gas analyzer for determining the concentrations of carbon dioxide, carbon monoxide, hydrocarbons, and nitrogen oxides in a sampled gas.
2. Description of Related Art
German Patent No. 967 633 describes a non-dispersive gas analyzer for determining carbon dioxide and carbon monoxide levels in a sampled gas. The gas analyzer operating by the dual beam principle has in each beam path a first measuring cell filled with sampled gas and traversed by an infrared beam, followed in sequence, in the direction of the beam, by an optopneumatic detector containing carbon monoxide, a second measuring cell filled with sampled gas, and an optopneumatic detector containing carbon dioxide.
From German Patent No. 39 37 141 A1 is known a non-dispersive infrared gas analyzer for determining levels of carbon dioxide, carbon monoxide, and methane, in which optopneumatic detectors are arranged in succession in the beam path downstream from the measuring cell, radiation filters being arranged between them, the detector immediately downstream from the measuring cell being filled with carbon monoxide, the next detector being filled with carbon dioxide, and the last detector being filled with methane.
Similarly, a non-dispersive infrared analyzer known from German Patent No. 25 05 006 C3 and U.S. Pat. No. 3,898,462 A has optopneumatic detectors, in the direction of the beam, downstream from the measuring cell, which in succession are filled with carbon monoxide, hydrocarbon, nitrogen oxide, and water vapor, respectively.
From German Patent No. 44 41 023 A it is known, in a non-dispersive infrared gas analyzer, to split a beam exiting from the measuring cell into a reflected and a transmitted partial beam using a beam splitter, the reflected partial beam being supplied to one detector for a certain gas component and the transmitted partial beam being supplied to another detector for another gas component or to another beam splitter. The beam splitter can be designed as an optical filter for the transmitted partial beam. Furthermore, the beam splitter can be arranged in a gas filter cell filled with an interfering gas.
In a similar infrared gas analyzer, known from German Patent No. 196 01 873 A1, an infrared beam is split into two partial beams by a beam splitter, the two components being passed through two different measuring cells filled with the sampled gas, and, upon exiting the measuring cells, being fed to different detectors for different gas components via additional beam splitters. In this context, the beam splitters are designed as optical filters for each transmitted partial beam.
An infrared gas analyzer known from German Patent No. A 44 03 763 has one single optopneumatic detector for determining the concentrations of a plurality of components such as carbon dioxide, carbon monoxide, and hydrocarbons in a sampled gas, the detector being filled with all the components to be analyzed. Filters are cyclically introduced in the path of the beam of the measuring cell that contains the sampled gas, an absorption range of one component falling within the passband range of each filter. On the basis of the detector output signals, which vary over time, the signal components to be associated with the individual gas components are determined, using signal analysis, as a function of the sequence in which the filters are introduced in the beam path.
In the aforementioned known gas analyzers, signal analysis is hindered by the fact that the individual components in the sampled gas not only absorb the infrared measuring light in different absorption ranges, but also do so with different intensities within those ranges. This is taken into account in the case of a non-dispersive infrared gas analyzer known from German Patent No. A 44 29 010 by passing the sampled gas through measuring cells of different lengths, each followed by an optopneumatic detector. Each detector contains one of the components to be analyzed, the length of the respective measuring cell being optimized to detect this component in the sampled gas. To pass the radiation through the parallel measuring cells, an infrared radiation emitter is made to pass by each measuring cell sequentially, making the construction of the gas analyzer relatively costly. The radiation cannot be passed through all the measuring cells simultaneously, since then each measuring cell would only receive a fraction of the total beam, which would no longer be sufficient for detection.